1. Field of the Invention
The present invention relates to heat resistant alloys having excellent high temperature carburization, oxidation (including cyclic oxidation) and sulfidation resistance.
2. Prior Art
It is well known that many industrial processes are operating at temperatures of up to 1800.degree. F. and above, and require equipment made of heat resistant alloys which will exhibit carburization, oxidation and sulfidation resistance at these temperatures. There is also a need for these alloys to have good welding characteristics so as to facilitate fabrication and maintenance of equipment.
One important industrial process that requires heat and corrosion resistant alloys is the production of ethylene by pyrolysis. This pyrolysis is carried out at high temperatures, usually in the range of 1600.degree. F. to 1800.degree. F. in tubular reactors. The combination of high temperature and a hydrocarbon stream produces an environment in which a very serious carburization problem results. As in all industrial processes, long-time maintenance-free operation is an economic necessity and, in this case, the severe carburization problem results in substantially reducing the serviceable life of the equipment unless a suitable alloy is used. Alloys for ethylene pyrolysis furnace tubes must also have good resistance to stresses that can induce creep and rupture at the operating temperatures and good resistance to oxidation and sulfidation attack, especially when impure feedstocks are used.
In addition, advancements in technology, e.g., higher operating temperatures, processing of lower grade feedstocks and the like, will impose more stringent service requirements upon alloys for this application and increase the demands for strong, more corrosion resistant alloys.
I have now discovered a new alloy providing a new combination of characteristics especially suitable in equipment for the production of ethylene by pyrolysis and for other equipment subjected to similar conditions of stress, temperature and corrosive attack.
It is an object of the invention to provide an alloy having a combination of characteristics including excellent resistance to carburization, oxidation, cyclic oxidation and sulfidation attack, good stress-rupture strength at high temperatures, and satisfactory weldability.
Another object of the invention is to provide heat and corrosion resistant alloy products and articles, including products and articles for use in ethylene pyrolysis furnace tubes.